Evidence presented in this proposal demonstrates that primary stimulation of frog liver cells with estrogenic steroid results in both new gene transcription followed by protein synthesis, and the replication of DNA followed by cell proliferation. Among the genes whose transcription increases in response to the hormone are: the vitellogenin genes, the c-myc cellular oncogene, and a gene for a protein of 45 K daltons, which could be creatine kinase. Our goal now is to describe specific molecular and biochemical changes taking place in liver cells which are likely to be important steps in the mechanism of steroid hormone initiation in cell proliferation. We suggest that estradiol-17Beta: A) Directly induces the trnascirption of particular genes including cmyc and E-p45, whose protein products are critical to the cell division process, and; B) Indirectly alters the metabolic activities of liver cells in favor of DNA replication via changing the pohosphorylated state of specific proteins. Three projects are proposed. I) Continued investigations of estradiol-17Beta induction of c-myc RNA and protein in the frog liver system. These studies will include an analysis of the kinetics of c-myc RNA induction both in vivo and in purified liver cells in culture, and its comparison to the RNAs for vitellogenin, c-ras, and c-src. II) Additional characterization of estrogen induction of the 45K protein, cloning of the RNA for this protein, and determination as to whether this protein i creatine kinase. III) Determination of the effects of estradiol-17Beta treatment on the pattern of intracellular phosphoproteins in liver cells and correlation of alterd patterns with entry of cells into the cell cycle. In order to carry out these studies we will take advatage of the estrogen responsive liver cell culture system we have developed. The results of these experiments are likely to be relevant to the general problem of how estrogens regulate normal cell growth and how they promote neoplastic transformation of cells previously exposed to a chemical carcinogen.